Worms in Dogs and Cats: Vet Guide to Worming, Symptoms and Prevention
Most pets will encounter worms at some point in their lives, particularly if they spend time outdoors.
Although many infections are mild, worms can sometimes cause symptoms such as digestive problems, weight loss and illness if left untreated. The good news is that most worm infections in dogs and cats are easy to treat and prevent with regular worming medication.
This guide explains how pets get worms, the symptoms to look for and how worm infections are treated and prevented.
Written by Gill Burkhill, Veterinary Surgeon, Animal Trust Vets CIC | Published April 2026 | Review date April 2029 | This advice is for UK pets only and is not a replacement for seeing a vet
What Types of Worms Affect Dogs and Cats?
The most common worms affecting pets in the UK include:
Roundworms
Roundworms are the most common intestinal parasite in both dogs and cats, particularly in puppies and kittens. The most common roundworms affecting pets belong to the Toxocara group.
Pets can become infected by:
Drinking infected milk from their mother
Eating infected prey such as rodents
Contact with contaminated soil or faeces
Symptoms may include:
A pot-bellied appearance (especially in young animals)
Vomiting worms
Poor growth in puppies or kittens
Tapeworms
Tapeworm infections usually occur when pets swallow infected fleas, but dogs and cats may also pick them up from eating rodents or other prey animals.
Signs may include:
Small white segments around the anus or in bedding
Scooting or irritation around the tail
Mild digestive upset
Controlling fleas is an important part of preventing tapeworm infections.
Lungworm in dogs
Lungworm is a parasite that affects the lungs and blood vessels of dogs. The main species affecting dogs in the UK is Angiostrongylus vasorum.
Dogs usually become infected with lungworm after eating slugs or snails, but they can also pick up the parasite from slug or snail slime left on grass, toys, food bowls or outdoor water bowls.
Symptoms may include:
Lungworm infections require prompt veterinary treatment because they can cause serious illness.
Diagnosis, Treatment and Prevention of Worms in Cats and Dogs
How do pets get worms?
Dogs and cats can pick up worms in several ways:
Hunting and eating prey
Swallowing infected fleas
Eating contaminated soil, grass or faeces
Drinking infected milk as puppies or kittens
Pets that spend time outdoors are generally at higher risk, but indoor pets can still become infected. For example, cats may swallow infected fleas brought into the home or occasionally catch rodents indoors.
How are worms diagnosed?
Sometimes worms or worm segments are visible in faeces or around the tail.
In other cases, a vet may recommend:
A faecal test to check for parasite eggs
Assessment of symptoms and lifestyle risk factors
Treatment for worms in dogs and cats
Most worm infections are treated using veterinary-approved worming medication.
Treatment may involve:
Oral tablets or liquid
Spot-on treatments
Repeat dosing to eliminate immature worms
Your vet will recommend the most appropriate treatment depending on the type of parasite involved.
How to prevent worms in dogs and cats
You can reduce the risk of worms by:
Following a regular worming schedule
Using effective flea control
Preventing pets from scavenging or hunting where possible
Cleaning litter trays and outdoor areas regularly
How Often Should Pets be Wormed?
Worming schedules vary depending on your pet’s age and lifestyle. Your vet can recommend a schedule for your pet.
Typical guidance includes:
Puppies and kittens
Wormed every 2-3 weeks until 12 weeks of age
Then regularly until adults
Adult dogs and cats
Usually, every 1-3 months depending on risk factors such as hunting, raw feeding or outdoor access
Your Animal Trust vet can advise on the most suitable parasite prevention plan for your pet.
Can pet worms infect humans?
Some worms carried by pets can occasionally infect people, although this is uncommon. Good hygiene helps reduce the risk:
Wash hands after handling pets
Pick up dog faeces promptly
Clean litter trays regularly
Follow regular worming programmes